This invention relates to resonant converters of the type which are commonly used for converting one source of electrical energy to another source having predetermined characteristics. Such resonant converters are well generally comprise a series resonant circuit, through which current is switched alternately in opposite directions at a frequency close to the resonant frequency of the circuit; an output is developed across one element of the resonant circuit, with an amplitude that can be controlled in accordance with the switching frequency.
These known resonant converters have the disadvantage that control of an output current by controlling the switching frequency will normally only permit an output current reduction down to about 5% of a nominal output current, and thus current reduction from nominal down to zero is not feasible. Moreover, wide switching frequency variations, say from 20 kHz to 60 kHz, produce a correspondingly wide variation in noise which is undesirable for some applications wherein a predictable noise spectrum associated with a constant switching frequency would be an advantage.
It is, therefore, an object of the present invention to provide a resonant converter in which the foregoing shortcomings of the known converters are obviated or diminished.